Mixing can be described as either distributive or dispersive. In a multi-phase material comprising discrete domains of each phase, distributive mixing seeks to change the relative spatial positions of the domains of each phase, whereas dispersive mixing seeks to overcome cohesive forces to alter the size and size distribution of the domains of each phase. Most mixers employ a combination of distributive or dispersive mixing although, depending on the intended application the balance will alter. For example a machine for mixing peanuts and raisins will be wholly distributive so as not to damage the things being mixed, whereas a blender/homogeniser will be dispersive.
Many different types of rotor/stator mixer are known. Stirring reactors such as those disclosed in US 2003/0139543 comprise a vessel with internally mounted mixing elements and are generally distributive in function. Other types of rotor-stator mixer (such as that disclosed in WO 2007/105323 are designed with the intention of forming fine emulsions and are dispersive in character.
EP 194 812 A2 discloses a cavity transfer mixer (CTM). Also WO 96/20270 describes a ‘Cavity Transfer Mixer’, comprising confronting surfaces, each having a series of cavities formed therein in which the surfaces move relatively to each other and in which a liquid material is passed between the surfaces and flows along a pathway successively passing through the cavities in each surface. The cavities are arranged on the relevant surfaces such that shear is applied to the liquid as it flows between the surfaces. In a typical embodiment the mixer comprises an outer sleeve and a close-fitting inner drum. The confronting surfaces of the sleeve and the drum are both provided with cavities disposed so that the cavities overlap forming sinuous and changing flow paths which change as the drum and the sleeve rotate relative to each other. This type of mixer has stator and rotor elements with opposed cavities which, as the mixer operates, move past each other across the direction of bulk flow through the mixer. In such mixers, primarily distributive mixing is obtained. Shear is applied by the relative movement of the surfaces in a generally perpendicular direction to the flow of material. In the typical embodiment described above, this is accomplished by relative rotation of the drum and the sleeve. In such a device there is relatively little variation in the cross-sectional area for flow as the material passes axially down the device. Generally, the cross-sectional area for flow varies by a factor of less than 3 through the apparatus.
WO 96/20270 also describes a novel mixer, hereinafter referred to as a ‘Controlled Deformation Dynamic Mixer’ (CDDM). In common with the CTM, type of mixer has stator and rotor elements with opposed cavities which, as the mixer operates, move past each other across the direction of bulk flow through the mixer. It is distinguished from the CTM in that material is also subjected to extensional deformation. The extensional flow and efficient dispersive mixing is secured by having confronting surfaces with cavities arranged such that the cross sectional area for bulk flow of the liquid through the mixer successively increases and decreases by a factor of at least 5 through the apparatus. In comparison with the embodiment of the CTM described above, the cavities of the CDDM are generally aligned or slightly offset in an axial direction such that material flowing axially along the confronting surfaces is forced through narrow gaps as well as flowing along and between the cavities. The CDDM combines the distributive mixing performance of the CTM with dispersive mixing performance. Thus, the CDDM is better suited to problems such as reducing the droplet size of an emulsion, where dispersive mixing is essential.
U.S. Pat. No. 6,468,578 B1 discloses the use of a cavity transfer mixer for creating an emulsion of water droplets in a continuous fat phase.
WO 2010/089320 A1, WO 2010/089322 A1, and WO 2010/091983 A1 disclose specific types of a distributive and dispersive mixing apparatus of the CDDM type or CTM type, comprising two confronting surfaces having cavities therein. These specific types may be used for the treatment of emulsions.
WO 2010/105922 A1 discloses that water-continuous emulsions of 5% silicone wax can be made in an aqueous solution that contains PET-POET polymer as emulsifier, by using a microfluidizer. This microfluidizer operates at high pressures of 1,200 bar to homogenise emulsions.
WO 96/28045 discloses a mixer with distributive and dispersive mixing zones, for making chewing gum.
US 2010/220545 A1 discloses a mixer with distributive and dispersive action, that can be used for emulsification.
WO 2008/125380 A1 discloses edible fat continuous spreads comprising phytosterols which are present in the form of elongated crystals, wherein the longest dimension is most preferably 2,000 micrometer.
WO 93/05768 and WO00/67728 disclose solid lipid particles having a diameter between 10 nanometer and 10 micrometer. These are produced by melting a lipid phase in an aqueous phase and subsequent homogenisation using a high pressure homogeniser.